Method for indicating a ciphering indication for a sidelink radio bearer in a d2d communication system and device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for indicating a ciphering indication for a sidelink radio bearer in a D2D communication system, the method comprising: receiving a PDCP SDU when the UE is configured to communicate with one or more other UEs directly; deciding whether to apply ciphering or not for the received PDCP SDU; generating a PDCP data PDU including the received PDCP SDU and a PDCP PDU header including one or more fields for ciphering parameters; and transmitting the PDCP data PDU to the one or more other UEs over PC5 interface, wherein at least one of the one or more fields for ciphering parameters is set to a fixed value when the ciphering is not applied for the received PDCP SDU.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119(e), this application claims the benefit ofU.S. Provisional Patent Application No. 62/077,326, filed on Nov. 10,2014, the contents of which are hereby incorporated by reference hereinin its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system and,more particularly, to a method for indicating a ciphering indication fora sidelink radio bearer in a D2D (Device to Device) communication systemand a device therefor.

Discussion of the Related Art

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Device to device (D2D) communication refers to the distributedcommunication technology that directly transfers traffic betweenadjacent nodes without using infrastructure such as a base station. In aD2D communication environment, each node such as a portable terminaldiscovers user equipment physically adjacent thereto and transmitstraffic after setting communication session. In this way, since D2Dcommunication may solve traffic overload by distributing trafficconcentrated into the base station, the D2D communication may havereceived attention as the element technology of the next generationmobile communication technology after 4G. For this reason, the standardinstitute such as 3GPP or IEEE has proceeded to establish the D2Dcommunication standard on the basis of LTE-A or Wi-Fi, and Qualcomm hasdeveloped their own D2D communication technology.

It is expected that the D2D communication contributes to increasethroughput of a mobile communication system and create new communicationservices. Also, the D2D communication may support proximity based socialnetwork services or network game services. The problem of link of a userequipment located at a shade zone may be solved by using a D2D link as arelay. In this way, it is expected that the D2D technology will providenew services in various fields.

The D2D communication technologies such as infrared communication,ZigBee, radio frequency identification (RFID) and near fieldcommunications (NFC) based on the RFID have been already used. However,since these technologies support communication only of a specific objectwithin a limited distance (about 1m), it is difficult for thetechnologies to be regarded as the D2D communication technologiesstrictly.

Although the D2D communication has been described as above, details of amethod for transmitting data from a plurality of D2D user equipmentswith the same resource have not been suggested.

SUMMARY OF THE INVENTION

The object of the present invention can be achieved by providing amethod for operating by an apparatus in wireless communication system,the method comprising; the method comprising: receiving a PDCP (PacketData Convergence Protocol) SDU (Service Data Unit) when the UE isconfigured to communicate with one or more other UEs directly; decidingwhether to apply ciphering or not for the received PDCP SDU; generatinga PDCP data PDU (Protocol Data Unit) including the received PDCP SDU anda PDCP PDU header including one or more fields for ciphering parameters;and transmitting the PDCP data PDU to the one or more other UEs over PC5interface, wherein at least one of the one or more fields for cipheringparameters is set to a fixed value when the ciphering is not applied forthe received PDCP SDU, and wherein the one or more field for cipheringparameters are set to values used for ciphering of the PDCP SDU when theciphering is applied for the received PDCP SDU.

In another aspect of the present invention provided herein is a methodfor operating by an apparatus in wireless communication system, themethod comprising: receiving a PDCP (Packet Data Convergence Protocol)SDU (Service Data Unit) when the UE is configured to communicate withone or more other UEs directly; deciding whether to apply ciphering ornot for the received PDCP SDU; generating a PDCP data PDU including anindicator indicating the PDCP data PDU is ciphered and parameters usedfor the ciphering if the ciphering is applied for the received PDCP SDU.

Preferably, the method further comprises: generating the PDCP data PDUincluding an indicator indicating the PDCP data PDU is not ciphered butdoesn't include the parameters used for the ciphering if the cipheringis not applied for the received PDCP SDU.

Preferably, the indicator is a Ciphering Indicator (CIND).

Preferably, the indicator is a SDU type field.

In another aspect of the present invention provided herein is a methodfor operating by an apparatus in wireless communication system, themethod comprising: receiving a PDCP (Packet Data Convergence Protocol)data PDU (Protocol Data Unit) from a peer UE over PC5 interface, whereinthe PDCP data PDU includes a PDCP SDU (Service Data Unit) and a PDCP PDUheader including one or more fields for ciphering parameters; anddetermining whether to apply deciphering or not for the PDCP data PDUaccording to values in the one or more fields for ciphering parameters;reassembling the PDCP SDU from the PDCP data PDU without deciphering thePDCP data PDU if the one or more fields for ciphering parameters is setto a fixed value; and reassembling the PDCP SDU from the PDCP data PDUafter deciphering the PDCP data PDU if the one or more field forciphering parameters are set to values different from the fixed value.

In another aspect of the present invention provided herein is a methodfor operating by an apparatus in wireless communication system, themethod comprising: receiving a PDCP (Packet Data Convergence Protocol)data PDU (Protocol Data Unit) from a peer UE over PC5 interface, whereinthe PDCP data PDU includes an indicator indicating the PDCP data PDU isciphered or not; and determining whether to apply deciphering or not forthe PDCP data PDU according to the indicator; reassembling the PDCP SDUfrom the PDCP data PDU after deciphering the PDCP data PDU by usingciphering parameters include in the PDCP data PDU if the indicatorindicates the PDCP data PDU is ciphered.

Preferably, the method further comprises: reassembling the PDCP SDU fromthe PDCP data PDU without deciphering the PDCP data PDU if the indicatorindicates the PDCP data PDU is not ciphered, wherein the PDCP data PDUdoesn't includes the ciphering parameters.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in anE-UMTS system;

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention

FIG. 6 is an example of default data path for a normal communication;

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication;

FIG. 9 is a conceptual diagram illustrating for a non-roaming referencearchitecture;

FIG. 10 is a conceptual diagram illustrating for a Layer 2 Structure forSidelink;

FIG. 11A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 11B is Control-Planeprotocol stack for ProSe Direct Communication;

FIG. 12 is a conceptual diagram illustrating for a PC5 interface forProSe Direct Discovery;

FIG. 13 is a diagram for a general overview of the LTE protocolarchitecture for the downlink;

FIG. 14 is a conceptual diagram for a PDCP entity architecture;

FIG. 15 is a conceptual diagram for functional view of a PDCP entity;

FIG. 16A is a format of the PDCP Data PDU carrying data for controlplane SRBs, FIG. 16B is a format of the PDCP Data PDU when a 12 bit SNlength is used, and FIG. 16C is a format of the PDCP Data PDU when a 7bit SN length is used;

FIG. 17 is a format of PDCP Data PDU format for SLRB.

FIG. 18 is a diagram for indicating a ciphering indication for asidelink radio bearer according to embodiments of the present invention;

FIGS. 19A and 19B are examples for indicating a ciphering indication fora sidelink radio bearer according to embodiments of the presentinvention;

FIGS. 20A and 20B are examples for indicating a ciphering indication fora sidelink radio bearer according to embodiments of the presentinvention;

FIG. 21 is a diagram for indicating a ciphering indication for asidelink radio bearer according to embodiments of the present invention;and

FIGS. 22A and 22B are examples for indicating a ciphering indication fora sidelink radio bearer according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is lms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is a block diagram of a communication apparatus according to anembodiment of the present invention.

The apparatus shown in FIG. 5 can be a user equipment (UE) and/or eNBadapted to perform the above mechanism, but it can be any apparatus forperforming the same operation.

As shown in FIG. 5, the apparatus may comprises a DSP/microprocessor(110) and RF module (transmiceiver; 135). The DSP/microprocessor (110)is electrically connected with the transciver (135) and controls it. Theapparatus may further include power management module (105), battery(155), display (115), keypad (120), SIM card (125), memory device (130),speaker (145) and input device (150), based on its implementation anddesigner's choice.

Specifically, FIG. 5 may represent a UE comprising a receiver (135)configured to receive a request message from a network, and atransmitter (135) configured to transmit the transmission or receptiontiming information to the network. These receiver and the transmittercan constitute the transceiver (135). The UE further comprises aprocessor (110) connected to the transceiver (135: receiver andtransmitter).

Also, FIG. 5 may represent a network apparatus comprising a transmitter(135) configured to transmit a request message to a UE and a receiver(135) configured to receive the transmission or reception timinginformation from the UE. These transmitter and receiver may constitutethe transceiver (135). The network further comprises a processor (110)connected to the transmitter and the receiver. This processor (110) maybe configured to calculate latency based on the transmission orreception timing information.

FIG. 6 is an example of default data path for communication between twoUEs. With reference to FIG. 6, even when two UEs (e.g., UE1, UE2) inclose proximity communicate with each other, their data path (userplane) goes via the operator network. Thus a typical data path for thecommunication involves eNB(s) and/or Gateway(s) (GW(s)) (e.g., SGW/PGW).

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication. If wireless devices (e.g., UE1, UE2) are in proximity ofeach other, they may be able to use a direct mode data path (FIG. 7) ora locally routed data path (FIG. 8). In the direct mode data path,wireless devices are connected directly each other (after appropriateprocedure(s), such as authentication), without eNB and SGW/PGW. In thelocally routed data path, wireless devices are connected each otherthrough eNB only.

FIG. 9 is a conceptual diagram illustrating for a non-roaming referencearchitecture.

PC1 to PC5 represent interfaces. PC1 is a reference point between aProSe application in a UE and a ProSe App server. It is used to defineapplication level signaling requirements. PC2 is a reference pointbetween the ProSe App Server and the ProSe Function. It is used todefine the interaction between ProSe App Server and ProSe functionalityprovided by the 3GPP EPS via ProSe Function. One example may be forapplication data updates for a ProSe database in the ProSe Function.Another example may be data for use by ProSe App Server in interworkingbetween 3GPP functionality and application data, e.g. name translation.PC3 is a reference point between the UE and ProSe Function. It is usedto define the interaction between UE and ProSe Function. An example maybe to use for configuration for ProSe discovery and communication. PC4is a reference point between the EPC and ProSe Function. It is used todefine the interaction between EPC and ProSe Function. Possible usecases may be when setting up a one-to-one communication path between UEsor when validating ProSe services (authorization) for session managementor mobility management in real time.

PC5 is a reference point between UE to UE used for control and userplane for discovery and communication, for relay and one-to-onecommunication (between UEs directly and between UEs over LTE-Uu).Lastly, PC6 is a reference point may be used for functions such as ProSeDiscovery between users subscribed to different PLMNs.

EPC (Evolved Packet Core) includes entities such as MME, S-GW, P-GW,PCRF, HSS etc. The EPC here represents the E-UTRAN Core Networkarchitecture. Interfaces inside the EPC may also be impacted albeit theyare not explicitly shown in FIG. 9.

Application servers, which are users of the ProSe capability forbuilding the application functionality, e.g. in the Public Safety casesthey can be specific agencies (PSAP) or in the commercial cases socialmedia. These applications are defined outside the 3GPP architecture butthere may be reference points towards 3GPP entities. The Applicationserver can communicate towards an application in the UE.

Applications in the UE use the ProSe capability for building theapplication functionality. Example may be for communication betweenmembers of Public Safety groups or for social media application thatrequests to find buddies in proximity. The ProSe Function in the network(as part of EPS) defined by 3GPP has a reference point towards the ProSeApp Server, towards the EPC and the UE.

The functionality may include but not restricted to e.g.:

Interworking via a reference point towards the 3rd party Applications

Authorization and configuration of the UE for discovery and Directcommunication

Enable the functionality of the EPC level ProSe discovery

ProSe related new subscriber data and /handling of data storage; alsohandling of ProSe identities;

Security related functionality

Provide Control towards the EPC for policy related functionality

Provide functionality for charging (via or outside of EPC, e.g. offlinecharging)

Especially, the following identities are used for ProSe DirectCommunication:

Source Layer-2 ID identifies a sender of a D2D packet at PC5 interface.The Source Layer-2 ID is used for identification of the receiver RLC UMentity;

Destination Layer-2 ID identifies a target of the D2D packet at PC5interface. The Destination Layer-2 ID is used for filtering of packetsat the MAC layer. The Destination Layer-2 ID may be a broadcast,groupcast or unicast identifier; and

SA L1 ID identifier in Scheduling Assignment (SA) at PC5 interface. SAL1 ID is used for filtering of packets at the physical layer. The SA L1ID may be a broadcast, groupcast or unicast identifier.

No Access Stratum signaling is required for group formation and toconfigure Source Layer-2 ID and Destination Layer-2 ID in the UE. Thisinformation is provided by higher layers.

In case of groupcast and unicast, the MAC layer will convert the higherlayer ProSe ID (i.e. ProSe Layer-2 Group ID and ProSe UE ID) identifyingthe target (Group, UE) into two bit strings of which one can beforwarded to the physical layer and used as SA L1 ID whereas the otheris used as Destination Layer-2 ID. For broadcast, L2 indicates to L1that it is a broadcast transmission using a pre-defined SA L1 ID in thesame format as for group- and unicast.

FIG. 10 is a conceptual diagram illustrating for a Layer 2 structure forSidelink.

The Sidelink is UE to UE interface for ProSe direct communication andProSe Direct Discovery. Corresponds to the PC5 interface. The Sidelinkcomprises ProSe Direct Discovery and ProSe Direct Communication betweenUEs. The Sidelink uses uplink resources and physical channel structuresimilar to uplink transmissions. However, some changes, noted below, aremade to the physical channels. E-UTRA defines two MAC entities; one inthe UE and one in the E-UTRAN. These MAC entities handle the followingtransport channels additionally, i) sidelink broadcast channel (SL-BCH),ii) sidelink discovery channel (SL-DCH) and iii) sidelink shared channel(SL-SCH).

Basic transmission scheme: the Sidelink transmission uses the same basictransmission scheme as the UL transmission scheme. However, sidelink islimited to single cluster transmissions for all the sidelink physicalchannels. Further, sidelink uses a 1 symbol gap at the end of eachsidelink sub-frame.

Physical-layer processing: the Sidelink physical layer processing oftransport channels differs from UL transmission in the following steps:

i) Scrambling: for PSDCH and PSCCH, the scrambling is not UE-specific;

ii) Modulation: 64 QAM is not supported for Sidelink.

Physical Sidelink control channel: PSCCH is mapped to the Sidelinkcontrol resources. PSCCH indicates resource and other transmissionparameters used by a UE for PSSCH.

Sidelink reference signals: for PSDCH, PSCCH and PSSCH demodulation,reference signals similar to uplink demodulation reference signals aretransmitted in the 4th symbol of the slot in normal CP and in the 3rdsymbol of the slot in extended cyclic prefix. The Sidelink demodulationreference signals sequence length equals the size (number ofsub-carriers) of the assigned resource. For PSDCH and PSCCH, referencesignals are created based on a fixed base sequence, cyclic shift andorthogonal cover code.

Physical channel procedure: for in-coverage operation, the powerspectral density of the sidelink transmissions can be influenced by theeNB.

FIG. 11A is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 11B is Control-Planeprotocol stack for ProSe Direct Communication.

FIG. 11A shows the protocol stack for the user plane, where PDCP, RLCand MAC sublayers (terminate at the other UE) perform the functionslisted for the user plane (e.g. header compression, HARQretransmissions). The PC5 interface consists of PDCP, RLC, MAC and PHYas shown in FIG. 11A.

User plane details of ProSe Direct Communication: i) MAC sub headercontains LCIDs (to differentiate multiple logical channels), ii) The MACheader comprises a Source Layer-2 ID and a Destination Layer-2 ID, iii)At MAC Multiplexing/demultiplexing, priority handling and padding areuseful for ProSe Direct communication, iv) RLC UM is used for ProSeDirect communication, v) Segmentation and reassembly of RLC SDUs areperformed, vi) A receiving UE needs to maintain at least one RLC UMentity per transmitting peer UE, vii) An RLC UM receiver entity does notneed to be configured prior to reception of the first RLC UM data unit,and viii) U-Mode is used for header compression in PDCP for ProSe DirectCommunication.

FIG. 11B shows the protocol stack for the control plane, where RRC, RLC,MAC, and PHY sublayers (terminate at the other UE) perform the functionslisted for the control plane. A D2D UE does not establish and maintain alogical connection to receiving D2D UEs prior to a D2D communication.

FIG. 12 is a conceptual diagram illustrating for a PC5 interface forProSe Direct Discovery.

ProSe Direct Discovery is defined as the procedure used by theProSe-enabled UE to discover other ProSe-enabled UE(s) in its proximityusing E-UTRA direct radio signals via PC5.

Radio Protocol Stack (AS) for ProSe Direct Discovery is shown in FIG.12.

The AS layer performs the following functions:

Interfaces with upper layer (ProSe Protocol): The MAC layer receives thediscovery information from the upper layer (ProSe Protocol). The IPlayer is not used for transmitting the discovery information.

Scheduling: The MAC layer determines the radio resource to be used forannouncing the discovery information received from upper layer.

Discovery PDU generation: The MAC layer builds the MAC PDU carrying thediscovery information and sends the MAC PDU to the physical layer fortransmission in the determined radio resource. No MAC header is added.

There are two types of resource allocation for discovery informationannouncement.

Type 1: A resource allocation procedure where resources for announcingof discovery information are allocated on a non UE specific basis,further characterized by: i) The eNB provides the UE(s) with theresource pool configuration used for announcing of discoveryinformation. The configuration may be signalled in SIB, ii) The UEautonomously selects radio resource(s) from the indicated resource pooland announce discovery information, iii) The UE can announce discoveryinformation on a randomly selected discovery resource during eachdiscovery period.

Type 2: A resource allocation procedure where resources for announcingof discovery information are allocated on a per UE specific basis,further characterized by: i) The UE in RRC CONNECTED may requestresource(s) for announcing of discovery information from the eNB viaRRC, ii) The eNB assigns resource(s) via RRC, iii) The resources areallocated within the resource pool that is configured in UEs formonitoring.

For UEs in RRC IDLE, the eNB may select one of the following options:

The eNB may provide a Type 1 resource pool for discovery informationannouncement in SIB. UEs that are authorized for Prose Direct Discoveryuse these resources for announcing discovery information in RRC_IDLE.

The eNB may indicate in SIB that it supports D2D but does not provideresources for discovery information announcement. UEs need to enter RRCConnected in order to request D2D resources for discovery informationannouncement.

For UEs in RRC_CONNECTED,

A UE authorized to perform ProSe Direct Discovery announcement indicatesto the eNB that it wants to perform D2D discovery announcement.

The eNB validates whether the UE is authorized for ProSe DirectDiscovery announcement using the UE context received from MME.

The eNB may configure the UE to use a Type 1 resource pool or dedicatedType 2 resources for discovery information announcement via dedicatedRRC signaling (or no resource).

The resources allocated by the eNB are valid until a) the eNBde-configures the resource(s) by RRC signaling or b) the UE enters IDLE.(FFS whether resources may remain valid even in IDLE).

Receiving UEs in RRC_IDLE and RRC_CONNECTED monitor both Type 1 and Type2 discovery resource pools as authorized. The eNB provides the resourcepool configuration used for discovery information monitoring in SIB. TheSIB may contain discovery resources used for announcing in neighborcells as well.

FIG. 13 is a diagram for a general overview of the LTE protocolarchitecture for the downlink.

A general overview of the LTE protocol architecture for the downlink isillustrated in FIG. 13. Furthermore, the LTE protocol structure relatedto uplink transmissions is similar to the downlink structure in FIG. 13,although there are differences with respect to transport formatselection and multi-antenna transmission.

Data to be transmitted in the downlink enters in the form of IP packetson one of the SAE bearers (1301). Prior to transmission over the radiointerface, incoming IP packets are passed through multiple protocolentities, summarized below and described in more detail in the followingsections:

* Packet Data Convergence Protocol (PDCP, 1303) performs IP headercompression to reduce the number of bits necessary to transmit over theradio interface. The header-compression mechanism is based on ROHC, astandardized header-compression algorithm used in WCDMA as well asseveral other mobile-communication standards. PDCP (1303) is alsoresponsible for ciphering and integrity protection of the transmitteddata. At the receiver side, the PDCP protocol performs the correspondingdeciphering and decompression operations. There is one PDCP entity perradio bearer configured for a mobile terminal.

* Radio Link Control (RLC, 1305) is responsible forsegmentation/concatenation, retransmission handling, and in-sequencedelivery to higher layers. Unlike WCDMA, the RLC protocol is located inthe eNodeB since there is only a single type of node in the LTEradio-access-network architecture. The RLC (1305) offers services to thePDCP (1303) in the form of radio bearers. There is one RLC entity perradio bearer configured for a terminal.

There is one RLC entity per logical channel configured for a terminal,where each RLC entity is responsible for: i) segmentation,concatenation, and reassembly of RLC SDUs; ii) RLC retransmission; andiii) in-sequence delivery and duplicate detection for the correspondinglogical channel.

Other noteworthy features of the RLC are: (1) the handling of varyingPDU sizes; and (2) the possibility for close interaction between thehybrid-ARQ and RLC protocols. Finally, the fact that there is one RLCentity per logical channel and one hybrid-ARQ entity per componentcarrier implies that one RLC entity may interact with multiplehybrid-ARQ entities in the case of carrier aggregation.

The purpose of the segmentation and concatenation mechanism is togenerate RLC PDUs of appropriate size from the incoming RLC SDUs. Onepossibility would be to define a fixed PDU size, a size that wouldresult in a compromise. If the size were too large, it would not bepossible to support the lowest data rates. Also, excessive padding wouldbe required in some scenarios. A single small PDU size, however, wouldresult in a high overhead from the header included with each PDU. Toavoid these drawbacks, which is especially important given the verylarge dynamic range of data rates supported by LTE, the RLC PDU sizevaries dynamically.

In process of segmentation and concatenation of RLC SDUs into RLC PDUs,a header includes, among other fields, a sequence number, which is usedby the reordering and retransmission mechanisms. The reassembly functionat the receiver side performs the reverse operation to reassemble theSDUs from the received PDUs.

* Medium Access Control (MAC, 1307) handles hybrid-ARQ retransmissionsand uplink and downlink scheduling. The scheduling functionality islocated in the eNodeB, which has one MAC entity per cell, for bothuplink and downlink. The hybrid-ARQ protocol part is present in both thetransmitting and receiving end of the MAC protocol. The MAC (1307)offers services to the RLC (1305) in the form of logical channels(1309).

* Physical Layer (PHY, 611), handles coding/decoding,modulation/demodulation, multi-antenna mapping, and other typicalphysical layer functions. The physical layer (1311) offers services tothe MAC layer (1307) in the form of transport channels (1313).

FIG. 14 is a conceptual diagram for a PDCP entity architecture.

FIG. 14 represents one possible structure for the PDCP sublayer, but itshould not restrict implementation. Each RB (i.e. DRB and SRB, exceptfor SRBO) is associated with one PDCP entity. Each PDCP entity isassociated with one or two (one for each direction) RLC entitiesdepending on the RB characteristic (i.e. uni-directional orbi-directional) and RLC mode. The PDCP entities are located in the PDCPsublayer. The PDCP sublayer is configured by upper layers.

FIG. 15 is a conceptual diagram for functional view of a PDCP entity.

The PDCP entities are located in the PDCP sublayer. Several PDCPentities may be defined for a UE. PDCP entity uses the services providedby the RLC sublayer. PDCP is used for SRBs, DRBs, and SLRBs mapped onDCCH, DTCH, and STCH type of logical channels. PDCP is not used for anyother type of logical channels.

The Packet Data Convergence Protocol supports the following functions:i) header compression and decompression of IP data flows using the ROHCprotocol, ii) transfer of data (user plane or control plane), iii)maintenance of PDCP SNs, iv) in-sequence delivery of upper layer PDUs atre-establishment of lower layers, v) duplicate elimination of lowerlayer SDUs at re-establishment of lower layers for radio bearers mappedon RLC AM, vi) ciphering and deciphering of user plane data and controlplane data, vii) integrity protection and integrity verification ofcontrol plane data, viii) for RNs, integrity protection and integrityverification of user plane data, ix) timer based discard, and x)duplicate discarding.

FIG. 16A is a format of the PDCP Data PDU carrying data for controlplane SRBs, FIG. 16B is a format of the PDCP Data PDU when a 12 bit SNlength is used. This format is applicable for PDCP Data PDUs carryingdata from DRBs mapped on RLC AM or RLC UM. FIG. 16C is a format of thePDCP Data PDU when a 7 bit SN length is used. This format is applicablefor PDCP Data PDUs carrying data from DRBs mapped on RLC UM.

A PDCP PDU is a bit string that is byte aligned (i.e. multiple of 8bits) in length. Bit strings are represented by tables in which the mostsignificant bit is the leftmost bit of the first line of the table, theleast significant bit is the rightmost bit on the last line of thetable, and more generally the bit string is to be read from left toright and then in the reading order of the lines. The bit order of eachparameter field within a PDCP PDU is represented with the first and mostsignificant bit in the leftmost bit and the last and least significantbit in the rightmost bit.

PDCP SDUs are bit strings that are byte aligned (i.e. multiple of 8bits) in length. A compressed or uncompressed SDU is included into aPDCP PDU from the first bit onward.

The PDCP data PDU is used to convey: i) a PDCP SDU SN, ii) user planedata containing an uncompressed PDCP SDU, iii) user plane datacontaining a compressed PDCP SDU, iv) control plane data, or v) a MAC-Ifield for SRBs.

The PDCP control PDU is used to convey: i) a PDCP status reportindicating which PDCP SDUs are missing and which are not following aPDCP re-establishment, and ii) header compression control information,e.g. interspersed ROHC feedback.

The bits in parameters used in FIGS. 16A to 16C can be interpreted asfollows. The left most bit string is the first and most significant andthe right most bit is the last and least significant bit. Unlessotherwise mentioned, integers are encoded in standard binary encodingfor unsigned integers.

a) PDCP SN: length of the PDCP SN is 5, 7, 12, or 15 bits as indicatedin Table 1.

TABLE 1 Length Description 5 SRBs 7 DRBs, if configured by upper layers(pdcp-SN-Size [3]) 12 DRBs, if configured by upper layers (pdcp-SN-Size[3]) 15 DRBs, if configured by upper layers (pdcp-SN-Size [3])

b) Data: Data field includes uncompressed PDCP SDU (user plane data, orcontrol plane data) or compressed PDCP SDU (user plane data only.

c) MAC-I: length of MAC-I is 32 bits. The MAC-I field carries a messageauthentication code calculated. For control plane data that are notintegrity protected, the MAC-I field is still present and should bepadded with padding bits set to 0.

d) COUNT: length of COUNT is 32 bits. For ciphering and integrity aCOUNT value is maintained. The COUNT value is composed of a HFN and thePDCP SN. The length of the PDCP SN is configured by upper layers. Thesize of the HFN part in bits is equal to 32 minus the length of the PDCPSN

e) R: length of R is 1 bit. The is bit is reserved bit set to 0.Reserved bits shall be ignored by the receiver.

FIG. 17 is a format of PDCP Data PDU format for SLRB.

For Sidelink transmission, the Tx UE may follow the procedures withfollowing modifications: i) the requirements for maintaining Next PDCPTX SN and TX HFN are not applicable, ii) the Tx UE determines a PDCP SNensuring that a PDCP SN value is not reused with the same key, iii) theTx UE determines a new PTK Identity (which has not been previously usedtogether with the same PGK and PGK Identity in the UE), and a new PTKshall be derived from the PGK key taking the new PTK Identity into use,iv) the Tx UE performs the ciphering with PEK and COUNT derived fromPDCP SN, and v) the Tx UE performs the header compression only for IPPDUs.

For Sidelink reception, the UE may follow the procedures with followingmodifications: i) the requirements for maintaining Next_PDCP_RX_SN andRX_HFN are not applicable; ii) the Rx UE performs the deciphering withPEK and COUNT derived from received PDCP SN, and iii) the UE performsthe header decompression only for IP PDUs.

FIG. 17 shows the format of the PDCP Data PDU for SLRB where a 16 bit SNlength is used. The PDCP data PDU for SLRB is used to convey: a PDCP SDUSN, and PGK Index, PTK Identity, and ProSe PDU type for the SLRBs, anduser plane data containing an uncompressed PDCP SDU, or user plane datacontaining a compressed PDCP SDU, or control plane data; and a MAC-Ifield for SRBs.

For ProSe, the ciphering function includes both ciphering anddeciphering and is performed in PDCP. For the user plane, the data unitthat is ciphered is the data part of the PDCP PDU. The cipheringalgorithm and key to be used by the PDCP entity are configured by ProSeKey Management Function and the ciphering method shall be applied. TheProSe transmitting UE decides whether to enable the ciphering. Ifenabled, the security parameters including PGK Index, PTK Identity areincluded in the header of PDCP PDU.

Since the transmitting UE is responsible for security, if thetransmitting UE enables ciphering and does not inform the receiving UE,the receiving UE cannot know which PDCP Data PDU format is used in thetransmitting UE, i.e., ciphering is enabled or not.

FIG. 18 is a diagram for indicating a ciphering indication for asidelink radio bearer according to embodiments of the present invention.

It is invented that a ciphering indicator is included in each PDCP dataPDU transmitted in PC5 interface (SLRB). The ciphering indicator in thePDCP data PDU indicates whether the ciphering is applied to thecorresponding PDCP data PDU or not.

When the TX UE receives a PDCP SDU (S1801) from an upper layer, the TXUE decides whether to apply ciphering or not for the received PDCP SDU(S1803).

If the TX UE decides to apply ciphering for the received PDCP SDU, theUE generates a PDCP data PDU including an indicator indicating that thePDCP data PDU is ciphered and parameters used for the ciphering (S1805).If the ciphering is applied for the received PDCP SDU, the TX UEperforms ciphering of the PDCP SDU and generates a PDCP data PDU usingFormat A including ciphered PDCP SDU.

Preferably, the parameters used for the ciphering is PGK index, PTKidentity, PDCP SN, and so on.

After the step of S1805, the TX UE transmits the generated PDCP data PDUusing Format A to a RX UE via PC5 interface (S1807).

When the RX UE receives a PDCP data PDU using Format A from the TX UEvia PC5 interface, the RX UE identifies whether ciphering is applied ornot to the PDCP SDU in the received PDCP data PDU based on a cipheringindicator included in the received PDCP data PDU.

Preferably, the ciphering indicator can be used by a Ciphering Indicator(CIND) field, or a SDU type field.

When the indicator is a CIND filed, the TX UE sets a value of the CINDfield to 0 if ciphering is not applied to the data, and 1 if cipheringis applied to the data, vice versa.

When the indicator is a SDU type field, the TX UE sets value of the SDUtype to Table 2 or Table 3:

TABLE 2 Bit Description 000 IP, ciphering is not applied 001 IP,ciphering is applied 010 ARP, ciphering is not applied 011 ARP,ciphering is applied 100-111 reserved

TABLE 3 Bit Description 000 IP, header compression is not applied,ciphering is not applied 001 IP, header compression is applied,ciphering is not applied 010 IP, header compression is not applied,ciphering is applied 011 IP, header compression is applied, ciphering isapplied 100 ARP, ciphering is applied 101 ARP, ciphering is not applied110-111 reserved

If the ciphering indicator indicates that the ciphering is applied tothe PDCP SDU included in the received PDCP data PDU (i.e. a value of theCNID field is 1 or a value of the SDU type field is 001 or 011 of Table2), the RX UE parses the received PDCP data PDU assuming Format A, andreassembles the PDCP SDU from the PDCP data PDU after deciphering thePDCP data PDU by using ciphering parameters include in the PDCP data PDU(S1809). Because the RX UE cannot know whether the PDCP data PDU is usedby the Format A or another Format, the RX UE assumes the received PDCPdata PDU is used by the Format A if the ciphering indicator indicatesthat the ciphering is applied to the PDCP SDU included in the receivedPDCP data PDU.

Meanwhile, if the TX UE decides not to apply ciphering for the receivedPDCP SDU, the UE generates a PDCP data PDU including an indicatorindicating the PDCP data PDU is not ciphered but doesn't include theparameters used for the ciphering (S1811). If the ciphering is notapplied for the received PDCP SDU, the TX UE doesn't perform cipheringof the PDCP SDU and generates a PDCP data PDU using Format B includingunciphered PDCP SDU.

After the step of S1811, the TX UE transmits the generated PDCP Data PDUusing Format B to the RX UE via PC5 interface (S1813). If the cipheringindicator indicates that the ciphering is not applied to the PDCP SDUincluded in the received PDCP data PDU (i.e. CNID is 0 or SDU type fieldis 000, or 010 of Table 2), the RX UE parses the received PDCP data PDUassuming Format B, and reassembles the PDCP SDU from the PDCP data PDUwithout deciphering the PDCP data PDU (S1815).

After the step of S1809 or S1815, the RX UE delivers the reassembledPDCP SDU to the ProSe upper layer.

FIGS. 19A and 19B are examples for indicating a ciphering indication fora sidelink radio bearer according to embodiments of the presentinvention, and FIGS. 20A and 20B are examples for ciphering indicationfor a sidelink radio bearer according to embodiments of the presentinvention.

FIGS. 19A and 19B show examples for PDCP data PDU using a CIND field asthe ciphering indicator. FIG. 19A is an example of the Format A and FIG.19B is an example of the Format B.

FIGS. 20A and 20B show examples for PDCP data PDU using a SDU type fieldas the ciphering indicator. FIG. 20A is an example of the Format A andFIG. 20B is an example of the Format B.

FIG. 21 is a diagram for indicating a ciphering indication for asidelink radio bearer according to embodiments of the present invention.

In this case, the TX UE uses parameters for ciphering instead of theciphering indicator. When the TX UE receives a PDCP SDU (S2101), the TXUE decides whether to apply ciphering or not for the received PDCP SDU(S2103).

When the TX UE generates PDCP data PDU including the received PDCP SDUand a PDCP PDU header including one or more fields for cipheringparameters, if the TX UE decides to apply ciphering for the receivedPDCP SDU, the one or more field for ciphering parameters are set tovalues used for ciphering of the PDCP SDU (S2105).

If the ciphering is applied for the received PDCP SDU, the TX UEperforms ciphering of the PDCP SDU and generates a PDCP data PDUincluding ciphered PDCP SDU, wherein the one or more field for cipheringparameters are set to values used for ciphering of the PDCP SDU.

After the step of S2105, the TX UE transmits the generated PDCP data PDUto the RX UE via PC5 interface (S2107).

When the RX UE receives a PDCP data PDU from the TX UE over PC5interface, the RX UE reassembles the PDCP SDU from the PDCP data PDUafter deciphering the PDCP data PDU if the one or more field forciphering parameters are set to values different from a fixed value(S2109).

Preferably, the one or more field for ciphering parameters can be PGKindex, PTK identity, PDCP SN, and so on.

Preferably, the fixed value is ‘0 (zero)’.

Meanwhile, when the TX UE generates PDCP data PDU including the receivedPDCP SDU and a PDCP PDU header including one or more fields forciphering parameters, if the TX UE decides not to apply ciphering forthe received PDCP SDU, the one or more field for ciphering parametersare set to the fixed value (S2111).

If the ciphering is not applied for the received PDCP SDU, the TX UEdoesn't perform ciphering of the PDCP SDU and generates a PDCP Data PDUincluding deciphered PDCP SDU, wherein the one or more field forciphering parameters are set to the fixed value.

Preferably, the one or more field for ciphering parameters can be PGKindex, PTK identity, PDCP SN, and so on.

Preferably, the fixed value is ‘0 (zero)’.

After the step of S2111, the TX UE transmits the generated PDCP data PDUto the RX UE via PC5 interface (S2113).

When the RX UE receives a PDCP data PDU from the TX UE over PC5interface, the RX UE reassembles the PDCP SDU from the PDCP data PDUwithout deciphering the PDCP data PDU if the one or more fields forciphering parameters is set to the fixed value (S2115).

After the step of S2109 or S2115, the RX UE delivers the reassembledPDCP SDU to the ProSe upper layer.

FIG. 22A and 22B are examples for indicating a ciphering indication fora sidelink radio bearer according to embodiments of the presentinvention.

FIG. 22A shows an example of PDCP data PDU including one or more fieldfor ciphering parameters are set to values different from a fixed value,and FIG. 22B shows an example of PDCP data PDU including one or morefield for ciphering parameters are set to the fixed value. For example,if ciphering is not configured, PGK Index, PTK Identity, and PDCP SN canbe set to “0” in the PDCP PDU header. Or, if ciphering is configured,PGK Index, PTK Identity, and PDCP SN can be set to “0” in the PDCP PDUheader.

Table 4 indicates cases of length of PDCP SN. The length of PDCP SN is5, 7, 12, 15 or 16 bits. For SLRB, if ciphering is applied to the data,the TX UE sets PDCP SN to 16. For example, if ciphering is not appliedto the data, the TX UE sets PGK Index and PTK Index as ‘0’.

TABLE 4 Length Description 5 SRBs 7 DRBs, if configured by upper layers(pdcp-SN- Size [3]) 12 DRBs, if configured by upper layers (pdcp-SN-Size [3]) 15 DRBs, if configured by upper layers (pdcp-SN- Size [3]) 16SLRBs

The embodiments of the present invention described herein below arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

In the embodiments of the present invention, a specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with an MS may be performed by the BS, or networknodes other than the BS. The term ‘eNB’ may be replaced with the term‘fixed station’, ‘Node B’, ‘Base Station (BS)’, ‘access point’, etc.

The above-described embodiments may be implemented by various means, forexample, by hardware, firmware, software, or a combination thereof.

In a hardware configuration, the method according to the embodiments ofthe present invention may be implemented by one or more ApplicationSpecific Integrated Circuits (ASICs), Digital Signal Processors (DSPs),Digital Signal Processing Devices (DSPDs), Programmable Logic Devices(PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, or microprocessors.

In a firmware or software configuration, the method according to theembodiments of the present invention may be implemented in the form ofmodules, procedures, functions, etc. performing the above-describedfunctions or operations. Software code may be stored in a memory unitand executed by a processor. The memory unit may be located at theinterior or exterior of the processor and may transmit and receive datato and from the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

What is claimed is:
 1. A method for transmitting, by an apparatus, datain a wireless communication system, the method comprising: determiningwhether to apply ciphering to the data; generating a packet dataconvergence protocol (PDCP) data protocol data unit (PDU) including adata part for the data; and transmitting the PDCP data PDU, wherein thePDCP data PDU includes fields for ciphering parameters, and wherein thefields for ciphering parameters are set to have a fixed value based on adetermination that ciphering is not applied to the data.
 2. The methodaccording to claim 1, wherein the fields for ciphering parameters areset to values used for ciphering the data based on a determination thatciphering is applied to the data.
 3. The method according to claim 1,wherein the data is transmitted over a PC5 interface.
 4. The methodaccording to claim 1, wherein the fields for ciphering parametersinclude a ProSe group key (PGK) index field and a ProSe traffic key(PTK) identity field.
 5. The method according to claim 4, wherein thePGK index field and the PTK identity field is set to have 0 based on thedetermination that ciphering for the data is not applied.
 6. The methodaccording to claim 1, wherein the fields for ciphering parameters have afixed size irrespective of whether ciphering is applied to the data. 7.A method for receiving, by an apparatus, data in a wirelesscommunication system, the method comprising: receiving a packet dataconvergence protocol (PDCP) data protocol data unit (PDU) including adata part for the data; determining a value included in fields forciphering parameters; and obtaining the data from the PDCP data PDU,wherein the PDCP data PDU includes the fields for ciphering parameters,and wherein the data is obtained from the PDCP data PDU withoutdeciphering the data part of PDCP data PDU based on a determination thatthe fields for ciphering parameters have a fixed value.
 8. The methodaccording to claim 7, wherein the data is obtained from the PDCP dataPDU by deciphering the data part of the PDCP data PDU based on adetermination that the fields for ciphering parameters have valuesdifferent from the fixed value.
 9. The method according to claim 7,wherein the data is received over a PC5 interface.
 10. The methodaccording to claim 7, wherein the fields for ciphering parametersinclude a ProSe group key (PGK) index field and a ProSe traffic key(PTK) identity field.
 11. An apparatus for a wireless communicationsystem, the apparatus comprising: a processor; and a memory that isoperably connectable to the processor and that has stored thereoninstructions which, when executed, cause the processor to performoperations comprising: determining whether to apply ciphering to data;generating a packet data convergence protocol (PDCP) data protocol dataunit (PDU) including a data part for the data, and transmitting the PDCPdata PDU, wherein the PDCP data PDU includes fields for cipheringparameters, and wherein the operations comprises: setting the fields forciphering parameters to have a fixed value when ciphering is not appliedto the data.
 12. The apparatus according to claim 11, wherein theoperations comprises: setting the fields for ciphering parameters tohave values used for ciphering the data when ciphering is applied to thedata.
 13. The apparatus according to claim 11, wherein the operationscomprises: transmitting the data over a PC5 interface.
 14. The apparatusaccording to claim 11, wherein the fields for ciphering parametersinclude a ProSe group key (PGK) index field and a ProSe traffic key(PTK) identity field.
 15. The apparatus according to claim 14, whereinthe operations comprises: setting the PGK index field and the PTKidentity field to have 0 when ciphering is not applied to the data. 16.The apparatus according to claim 11, wherein the fields for cipheringparameters have a fixed size irrespective of whether ciphering isapplied to the data.
 17. An apparatus for a wireless communicationsystem, the apparatus comprising: a processor; and a memory that isoperably connectable to the processor and that has stored thereoninstructions which, when executed, cause the processor to performoperations comprising: receiving a packet data convergence protocol(PDCP) data protocol data unit (PDU) including a data part for the data;determining a value included in fields for ciphering parameters; andobtaining the data from the PDCP data PDU, wherein the PDCP data PDUincludes the fields for ciphering parameters, and wherein obtaining thedata comprises: obtaining the data from the PDCP data PDU withoutdeciphering the data part of the PDCP data PDU when the fields forciphering parameters have a fixed value.
 18. The apparatus according toclaim 17, wherein obtaining the data comprises: deciphering the datapart of the PDCP data PDU to obtain the data when the fields forciphering parameters have values different from the fixed value.
 19. Theapparatus according to claim 17, wherein the data is received over a PC5interface.
 20. The apparatus according to claim 17, wherein the fieldsfor ciphering parameters include a ProSe group key (PGK) index field anda ProSe traffic key (PTK) identity field.